Large capacity rechargeable batteries are currently being investigated for use in electric vehicles. The ultimate feasibility of electric vehicles depends on significantly reducing the associated costs. Reduction in the costs of battery assemblies is particularly important.
Lithium ion batteries are an important type of battery technology. Most battery assemblies, including lithium ion battery assemblies, include a plurality of individual electrochemical cells. A cell consists of an anode, cathode, porous separator film, and an ionically conductive but electrically isolative electrolyte. The voltage of the cell is dependent on the electrochemical potential of the cell chemistry, the current is dependent on the rate at which the ions shuttle between the anode and cathode, and the capacity depends on the total surface area of the cell. To maintain capacity over the life of the cell, it is important to apply pressure equally across the cell surface area. There are two primary designs for large amp hour capacity cells typically used in automotive application; cylindrical and prismatic. For cylindrical cells, pressure is maintained by the spiral nature of the cell design. For prismatic cells, uniform pressure is maintained by means of foam or spring loaded plate.
For high power application, a plurality of battery cells are utilized and assembled into a battery module. Moreover, such battery modules are assembled into battery packs which include a cooling system and related electronics for operating the batteries. The cooling systems typically include a plurality of air or liquid cooled metallic (e.g., copper and/or aluminum) fins interspersed between the battery cells, which must also maintain intimate contact with the cell for optimal heat transfer. Prior state of the art for the assembly of a battery module includes either stacking, or the mechanical pre-compression of the assembly prior to insertion into a module frame.
Accordingly, there is a need for improved battery module assembly designs and for methods of constructing such battery module assemblies.